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<ul id="index">
  <li><a href="#NAME">NAME</a></li>
  <li><a href="#SYNOPSIS">SYNOPSIS</a></li>
  <li><a href="#DESCRIPTION">DESCRIPTION</a></li>
  <li><a href="#NOTES">NOTES</a></li>
  <li><a href="#RETURN-VALUES">RETURN VALUES</a></li>
  <li><a href="#EXAMPLES">EXAMPLES</a></li>
  <li><a href="#SEE-ALSO">SEE ALSO</a></li>
  <li><a href="#HISTORY">HISTORY</a></li>
  <li><a href="#COPYRIGHT">COPYRIGHT</a></li>
</ul>

<h1 id="NAME">NAME</h1>

<p>EVP_PKEY_sign_init, EVP_PKEY_sign_init_ex, EVP_PKEY_sign - sign using a public key algorithm</p>

<h1 id="SYNOPSIS">SYNOPSIS</h1>

<pre><code>#include &lt;openssl/evp.h&gt;

int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx);
int EVP_PKEY_sign_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
int EVP_PKEY_sign(EVP_PKEY_CTX *ctx,
                  unsigned char *sig, size_t *siglen,
                  const unsigned char *tbs, size_t tbslen);</code></pre>

<h1 id="DESCRIPTION">DESCRIPTION</h1>

<p>EVP_PKEY_sign_init() initializes a public key algorithm context <i>ctx</i> for signing using the algorithm given when the context was created using <a href="../man3/EVP_PKEY_CTX_new.html">EVP_PKEY_CTX_new(3)</a> or variants thereof. The algorithm is used to fetch a <b>EVP_SIGNATURE</b> method implicitly, see <a href="../man7/provider.html">&quot;Implicit fetch&quot; in provider(7)</a> for more information about implicit fetches.</p>

<p>EVP_PKEY_sign_init_ex() is the same as EVP_PKEY_sign_init() but additionally sets the passed parameters <i>params</i> on the context before returning.</p>

<p>The EVP_PKEY_sign() function performs a public key signing operation using <i>ctx</i>. The data to be signed is specified using the <i>tbs</i> and <i>tbslen</i> parameters. If <i>sig</i> is NULL then the maximum size of the output buffer is written to the <i>siglen</i> parameter. If <i>sig</i> is not NULL then before the call the <i>siglen</i> parameter should contain the length of the <i>sig</i> buffer, if the call is successful the signature is written to <i>sig</i> and the amount of data written to <i>siglen</i>.</p>

<h1 id="NOTES">NOTES</h1>

<p>EVP_PKEY_sign() does not hash the data to be signed, and therefore is normally used to sign digests. For signing arbitrary messages, see the <a href="../man3/EVP_DigestSignInit.html">EVP_DigestSignInit(3)</a> and <a href="../man3/EVP_SignInit.html">EVP_SignInit(3)</a> signing interfaces instead.</p>

<p>After the call to EVP_PKEY_sign_init() algorithm specific control operations can be performed to set any appropriate parameters for the operation (see <a href="../man3/EVP_PKEY_CTX_ctrl.html">EVP_PKEY_CTX_ctrl(3)</a>).</p>

<p>The function EVP_PKEY_sign() can be called more than once on the same context if several operations are performed using the same parameters.</p>

<h1 id="RETURN-VALUES">RETURN VALUES</h1>

<p>EVP_PKEY_sign_init() and EVP_PKEY_sign() return 1 for success and 0 or a negative value for failure. In particular a return value of -2 indicates the operation is not supported by the public key algorithm.</p>

<h1 id="EXAMPLES">EXAMPLES</h1>

<p>Sign data using RSA with PKCS#1 padding and SHA256 digest:</p>

<pre><code>#include &lt;openssl/evp.h&gt;
#include &lt;openssl/rsa.h&gt;

EVP_PKEY_CTX *ctx;
/* md is a SHA-256 digest in this example. */
unsigned char *md, *sig;
size_t mdlen = 32, siglen;
EVP_PKEY *signing_key;

/*
 * NB: assumes signing_key and md are set up before the next
 * step. signing_key must be an RSA private key and md must
 * point to the SHA-256 digest to be signed.
 */
ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);
if (!ctx)
    /* Error occurred */
if (EVP_PKEY_sign_init(ctx) &lt;= 0)
    /* Error */
if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) &lt;= 0)
    /* Error */
if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) &lt;= 0)
    /* Error */

/* Determine buffer length */
if (EVP_PKEY_sign(ctx, NULL, &amp;siglen, md, mdlen) &lt;= 0)
    /* Error */

sig = OPENSSL_malloc(siglen);

if (!sig)
    /* malloc failure */

if (EVP_PKEY_sign(ctx, sig, &amp;siglen, md, mdlen) &lt;= 0)
    /* Error */

/* Signature is siglen bytes written to buffer sig */</code></pre>

<h1 id="SEE-ALSO">SEE ALSO</h1>

<p><a href="../man3/EVP_PKEY_CTX_new.html">EVP_PKEY_CTX_new(3)</a>, <a href="../man3/EVP_PKEY_CTX_ctrl.html">EVP_PKEY_CTX_ctrl(3)</a>, <a href="../man3/EVP_PKEY_encrypt.html">EVP_PKEY_encrypt(3)</a>, <a href="../man3/EVP_PKEY_decrypt.html">EVP_PKEY_decrypt(3)</a>, <a href="../man3/EVP_PKEY_verify.html">EVP_PKEY_verify(3)</a>, <a href="../man3/EVP_PKEY_verify_recover.html">EVP_PKEY_verify_recover(3)</a>, <a href="../man3/EVP_PKEY_derive.html">EVP_PKEY_derive(3)</a></p>

<h1 id="HISTORY">HISTORY</h1>

<p>The EVP_PKEY_sign_init() and EVP_PKEY_sign() functions were added in OpenSSL 1.0.0.</p>

<p>The EVP_PKEY_sign_init_ex() function was added in OpenSSL 3.0.</p>

<h1 id="COPYRIGHT">COPYRIGHT</h1>

<p>Copyright 2006-2021 The OpenSSL Project Authors. All Rights Reserved.</p>

<p>Licensed under the Apache License 2.0 (the &quot;License&quot;). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>


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